U.S. patent application number 12/379509 was filed with the patent office on 2009-09-10 for nonvolatile semiconductor storage device with charge storage layer and its manufacturing method.
This patent application is currently assigned to NEC Electronics Corporation. Invention is credited to Fumihiko Hayashi.
Application Number | 20090224306 12/379509 |
Document ID | / |
Family ID | 41052704 |
Filed Date | 2009-09-10 |
United States Patent
Application |
20090224306 |
Kind Code |
A1 |
Hayashi; Fumihiko |
September 10, 2009 |
Nonvolatile semiconductor storage device with charge storage layer
and its manufacturing method
Abstract
A nonvolatile semiconductor storage device includes a
semiconductor substrate, a charge storage layer formed above the
semiconductor substrate, a control gate formed above the charge
storage layer, a spacer layer formed above the control gate and a
word gate formed above a side of the control gate and the spacer
layer. Atop surface of the spacer layer is lower as the top surface
of the spacer layer is farther from the word gate.
Inventors: |
Hayashi; Fumihiko;
(Kanagawa, JP) |
Correspondence
Address: |
MCGINN INTELLECTUAL PROPERTY LAW GROUP, PLLC
8321 OLD COURTHOUSE ROAD, SUITE 200
VIENNA
VA
22182-3817
US
|
Assignee: |
NEC Electronics Corporation
Kawasaki
JP
|
Family ID: |
41052704 |
Appl. No.: |
12/379509 |
Filed: |
February 24, 2009 |
Current U.S.
Class: |
257/316 ;
257/E29.3 |
Current CPC
Class: |
H01L 29/40117 20190801;
H01L 29/792 20130101; H01L 29/7923 20130101; H01L 29/42344
20130101; H01L 29/42348 20130101 |
Class at
Publication: |
257/316 ;
257/E29.3 |
International
Class: |
H01L 29/788 20060101
H01L029/788 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 5, 2008 |
JP |
2008-055597 |
Claims
1. A nonvolatile semiconductor storage device, comprising: a
semiconductor substrate; a charge storage layer formed above the
semiconductor substrate; a control gate formed above the charge
storage layer; a spacer layer formed above the control gate; and a
word gate formed above a side of the control gate and the spacer
layer, wherein a top surface of the spacer layer is lower as the
top surface of the spacer layer is farther from the word gate.
2. The nonvolatile semiconductor storage device according to claim
1, wherein a top surface of the control gate is substantially
flat.
3. The nonvolatile semiconductor storage device according to claim
1, wherein a height of a top surface of the word gate from the
semiconductor substrate is higher than a height of a top surface of
the control gate from the semiconductor substrate.
4. The nonvolatile semiconductor storage device according to claim
1, wherein the charge storage layer includes: a first silicon oxide
layer; a silicon nitride layer formed above the first silicon oxide
layer; and a second silicon oxide layer formed above the silicon
nitride layer.
5. The nonvolatile semiconductor storage device according to claim
1, further comprising: a first diffusion layer formed on the
semiconductor substrate; and a second diffusion layer formed on the
semiconductor substrate, wherein the charge storage layer and the
word gate are disposed between the first diffusion layer and the
second diffusion layer.
6. The nonvolatile semiconductor storage device according to claim
5, further comprising: a first silicide layer formed on the word
gate; a second silicide layer formed on the first diffusion layer;
and a third silicide layer formed on the second diffusion
layer.
7. The nonvolatile semiconductor storage device according to claim
1, further comprising a silicide layer formed on a top surface of
the control gate.
8. The nonvolatile semiconductor storage device according to claim
6, further comprising a fourth silicide layer formed on a top
surface of the control gate.
9. The nonvolatile semiconductor storage device according to claim
1, wherein the charge storage layer comprises a first charge
storage layer, wherein the control gate comprises a first control
gate, wherein the spacer layer comprises a first spacer layer,
wherein the nonvolatile semiconductor storage device further
comprises: a second charge storage layer formed above the
semiconductor substrate, the first charge storage layer and the
second charge storage layer being disposed symmetrically with
respect to the word gate; a second control gate formed above the
second charge storage layer, the first control gate and the second
control gate being disposed symmetrically with respect to the word
gate; and a second spacer layer formed above the second control
gate, the first spacer layer and the second spacer layer being
disposed symmetrically with respect to the word gate, wherein a top
surface of the second spacer layer is lower as the top surface of
the second spacer layer is farther from the word gate.
10. The nonvolatile semiconductor storage device according to claim
9, further comprising: a first silicide layer formed on a top
surface of the first control gate; and a second silicide layer
formed on a top surface of the second control gate.
11. The nonvolatile semiconductor storage device according to claim
9, further comprising: a first diffusion layer formed on the
semiconductor substrate; and a second diffusion layer formed on the
semiconductor substrate, wherein the first charge storage layer,
the second charge storage layer and the word gate are disposed
between the first diffusion layer and the second diffusion
layer.
12. A nonvolatile semiconductor storage device, comprising: a
semiconductor substrate; a charge storage layer formed above the
semiconductor substrate; a control gate formed above the charge
storage layer; a spacer layer formed above the control gate; and a
word gate formed above a side of the control gate and the spacer
layer, wherein a width of the spacer layer is narrower as the width
of the spacer layer is farther from the control gate.
13. The nonvolatile semiconductor storage device according to
claim.12, wherein a top surface of the control gate is
substantially flat.
14. The nonvolatile semiconductor storage device according to claim
12, further comprising a silicide layer formed on a top surface of
the control gate.
15. The nonvolatile semiconductor storage device according to claim
12, wherein the charge storage layer comprises a first charge
storage layer, wherein the control gate comprises a first control
gate, wherein the spacer layer comprises a first spacer layer,
wherein the nonvolatile semiconductor storage device further
comprises: a second charge storage layer formed above the
semiconductor substrate, the first charge storage layer and the
second charge storage layer being disposed symmetrically with
respect to the word gate; a second control gate formed above the
second charge storage layer, the first control gate and the second
control gate being disposed symmetrically with respect to the word
gate; and a second spacer layer formed above the second control
gate, the first spacer layer and the second spacer layer being
disposed symmetrically with respect to the word gate, wherein a
width of the second spacer layer is narrower as the width of the
second spacer layer is farther from the second control gate.
16. The nonvolatile semiconductor storage device according to claim
15, further comprising: a first silicide layer formed on a top
surface of the first control gate; and a second silicide layer
formed on a top surface of the second control gate.
17. A nonvolatile semiconductor storage device, comprising: a
semiconductor substrate; a charge storage layer formed above the
semiconductor substrate; a control gate formed above the charge
storage layer; a spacer layer formed above the control gate; and a
word gate formed above a side of the control gate and the spacer
layer, wherein a height of the spacer layer from a top surface of
the control gate is lower as the top surface of the spacer layer is
farther from the word gate.
18. The nonvolatile semiconductor storage device according to claim
17, wherein a top surface of the control gate is substantially
flat.
19. The nonvolatile semiconductor storage device according to claim
17, further comprising a silicide layer formed on a top surface of
the control gate.
20. The nonvolatile semiconductor storage device according to claim
17, wherein the charge storage layer comprises a first charge
storage layer, wherein the control gate comprises a first control
gate, wherein the spacer layer comprises a first spacer layer,
wherein the nonvolatile semiconductor storage device further
comprises: a second charge storage layer formed above the
semiconductor substrate, the first charge storage layer and the
second charge storage layer being disposed symmetrically with
respect to the word gate; a second control gate formed above the
second charge storage layer, the first control gate and the second
control gate being disposed symmetrically with respect to the word
gate; and a second spacer layer formed above the second control
gate, the first spacer layer and the second spacer layer being
disposed symmetrically with respect to the word gate, wherein a
height of the spacer layer from a top surface of the second control
gate is lower as the top surface of the second spacer layer is
farther from the word gate.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is related to U.S. patent
application Ser. No. ______, concurrently filed herewith, and which
is based on Japanese Patent Application No. 2008-055598 filed on
Mar. 5, 2008.
INCORPORATION BY REFERENCE
[0002] This application is based upon and claims the benefit of
priority from Japanese Patent Application No. 2008-055597 which was
filed on Mar. 5, 2008, the disclosure of which is incorporated
herein in its entirety by reference.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates to a nonvolatile semiconductor
storage device and to a method of manufacturing the same, and more
particularly to a charge trap type nonvolatile semiconductor
storage device and to a method-of manufacturing the same.
[0005] 2. Description of Related Art
[0006] As the nonvolatile semiconductor storage device, there has
been known a charge trap-type nonvolatile semiconductor storage
device. For example, JP-A-2004-312009 (corresponding U.S. Patent:
U.S. Pat. No. 7,005,349B2) discloses a method of manufacturing a
silicon-oxide-nitride-oxide-silicon (SONOS) memory device.
[0007] FIGS. 1 to 9 are cross-sectional views showing the SONOS
memory device manufacturing method in JP-A-2004-312009. First, as
shown in FIG. 1, a dielectric layer 111 made of ONO
(oxide-nitride-oxide) is formed on a semiconductor substrate 110.
Then, a first conductive layer 130a is formed on the dielectric
layer 111. Thereafter, a buffer layer 180 is formed on the first
conductive layer 130a. Then, as shown in FIG. 2, a trench 181 from
which a partial surface of the first conductive layer 130a is
exposed is formed on the buffer layer 180. Subsequently, as shown
in FIG. 3, a first insulating film 117a is so formed as to cover
the trench 181.
[0008] Then, as shown in FIG. 4, the first insulting film 117a is
etched back to form a first insulating spacer 117 on an inner wall
of the trench 181. Thereafter, as shown in FIG. 5, an exposed
portion of the first conductive layer 130a and a portion of the
dielectric layer 111 therebelow are selectively sequentially
removed with the first insulating spacer as an etching mask,
thereby dividing the first conductive layer 130a and the dielectric
layer 111 into two portions, respectively.
[0009] Subsequently, as shown in FIG. 6, a gate dielectric layer
115 is formed on the semiconductor substrate 110 exposed by
separation of the dielectric layer 111. The gate dielectric layer
115 extends on the first insulating spacer 117 so as to insulate
the two first conductive layers 130a from each other so that the
two separated first conductive layers 130a below the first
insulating spacers 117 are allowed to function as independent gates
(control gates 130), respectively. Subsequently, a second
conductive layer 120 (word gate 120) embedded in a gap between both
side walls of the trench is formed on the gate dielectric layer
115. Then, a capping insulating layer 118 is so formed as to cover
the upper portion of the second conductive layer 120.
[0010] Then, as shown in FIG. 7, the buffer layer 180 is removed
with the first insulating spacer 117 as an etching mask.
Subsequently, as shown in FIG. 8, a portion of the first conductive
layer 130a which has been exposed by removal of the buffer layer
180, and a portion of the dielectric layer 111 therebelow are
selectively sequentially removed with the first insulating spacer
117 as an etching mask to provide the dielectric layer 111 and the
first conductive layer 130 (control gate 130) which have been
divided into two parts, respectively, as a final pattern.
[0011] Then, as shown in FIG. 9, a first diffusion layer 151a is
formed on the semiconductor substrate 110 exposed outside of the
final pattern (dielectric layer 111) by ion implantation. Then, a
second insulating spacer 116 is formed on the side walls of the
dielectric layer 111 and the first conductive layer 130 which are
the final pattern. Then, a second diffusion layer 151b is formed on
the semiconductor substrate 110 by ion implantation with the second
insulating spacer 116 as a mask. Thereafter, although being not
shown, a second silicide layer is selectively formed on the second
diffusion layer 151b, and a third silicide layer is formed on the
second conductive layer 120 in a silicide inducing process. The
first conductive layer and the second conductive layer are each
formed to include a conductive silicon layer.
[0012] Also, T. Saito et al., "Hot hole erase characteristics and
reliability in twin MONOS device", IEEE non-volatile semiconductor
memory workshop, pp. 50-52, 2003 discloses a device of a twin-MONOS
structure as a nonvolatile semiconductor memory device of a split
gate-type.
[0013] With the advanced miniaturization of a memory, various
characteristics required for write, erase, disturb, etc. have
become increasingly severe. In order to satisfy the
characteristics, the controllability of the gate length of the
control gate electrode is very important.
SUMMARY
[0014] However, in a technique (FIGS. 1 to 9) of JP-A-2004-312009
described above, the controllability of the gate length of the
control gate electrode can be deteriorated as has been proved by
the inventors' research. Hereinafter, the problem will be
described.
[0015] FIGS. 10 to 12 are cross-sectional views for explaining the
problems on the technique of JP-A-2004-312009. As shown in FIG. 10,
in etching for forming a trench 181 in FIG. 2, a buffer layer 180
has its side surface liable to be tapered. That is, a portion of a
side surface 180h at the semiconductor substrate 110 side is
configured to project toward the trench 181 side by .DELTA.1 from a
portion of the top surface side. In this case, as shown in FIG. 11,
a first insulating spacer 117 has its side surface 117h inversely
tapered in a first insulating spacer 117 formation process shown in
FIG. 4. That is, a portion of the side surface 117h at the
semiconductor substrate 110 side is configured to be recessed
toward the trench 181 side by .DELTA.2 (substantially equal to
.DELTA.1) from a portion of the top surface side.
[0016] Under the above circumstances, when a first conductive layer
130a (and a dielectric layer 111) is selectively sequentially
removed with the first insulating spacer 117 as an etching mask in
FIG. 8, there arises the following problem. As shown in FIG. 12,
the side surface 117h of the first insulating spacer 117 is
inversely tapered, and a width L2 of the first insulating spacer
117 at a bottom surface 117b side is shorter than a width L1 at an
top surface 117t side by .DELTA.3 (substantially equal to .DELTA.2)
(.DELTA.3=L1-L2). That is, the top surface 117t is configured to
project from the bottom surface 117b by .DELTA.3. When the first
conductive layer 130 is etched with the above first insulating
spacer 117 as a mask, it is conceivable that a width L4 of the
first conductive layer 130 at the top surface 130t side varies in a
range of from the width L1 of the first insulating spacer 117 at
the top surface 117t side to the width L2 at the bottom surface
117b side. That is, a gate length of the control gate 130 is
varied. The variation becomes larger as a thickness L3 of the first
insulating spacer 117 is thicker. This is because etching ions are
liable to go around to the inside of the inverse taper more as a
stroke of the etching ions from the top surface 117t of the first
insulating spacer 117 to the bottom surface 117b is longer (a
thickness L3 is thicker), and the go-around probability is
varied.
[0017] Further, the magnitude of .DELTA.1 of the taper in FIG. 10
is varied because of the control difficulty. That is, the above
variation can occur when the magnitude of .DELTA.1 is varied, or
when there is no variation per se. Correspondingly, in a stage of
FIG. 12, the above variation can occur when the magnitude of
.DELTA.3 in the inverse taper is varied, or when there is no
variation per se. Thus, even in this event, in addition to the
above case, the width L4 of the first conductive layer 130, that
is, the gate length of the control gate 130, is varied. As a
result, the memory cells are varied, and various characteristics
required for write, erase, disturb, and so on cannot be satisfied,
and a manufacture yield is also adversely affected. A technique for
suppressing a variation in the gate length of the control gate is
desired.
[0018] The present invention seeks to solve one or more of the
above problems, or to improve upon those problems at least in
part.
[0019] In one exemplary embodiment, a nonvolatile semiconductor
storage device according to the present invention includes a
semiconductor substrate, a charge storage layer formed above the
semiconductor substrate, a control gate formed above the charge
storage layer, a spacer layer formed above the control gate and a
word gate formed above a side of the control gate and the spacer
layer. Atop surface of the spacer layer is lower as the top surface
of the spacer layer is farther from the word gate.
[0020] In another exemplary embodiment, a nonvolatile semiconductor
storage device according to the present invention includes a
semiconductor substrate, a charge storage layer formed above the
semiconductor substrate, a control gate formed above the charge
storage layer, a spacer layer formed above the control gate, and a
word gate formed above a side of the control gate and the spacer
layer. A width of the spacer layer is narrower as the width of the
spacer layer is farther from the control gate.
[0021] In yet another exemplary embodiment, a nonvolatile
semiconductor storage device according to the present invention
includes a semiconductor substrate, a charge storage layer formed
above the semiconductor substrate, a control gate formed above the
charge storage layer, a spacer layer formed above the control gate
and a word gate formed above a side of the control gate and the
spacer layer. A height of the spacer layer from a top surface of
the control gate is lower as the top surface of the spacer layer is
farther from the word gate.
[0022] Thus, in the nonvolatile semiconductor storage device
according to the present invention, the spacer layer is lowered as
the spacer layer is farther from the word gate or is narrower as
the spacer layer is farther from the control gate. That is, the
side surface of the spacer layer is not of an inversely tapered
configuration in which the top surface side is projected from the
bottom surface side. Accordingly, in etching with the spacer layer
as a mask, the width of the control gate can be controlled by the
width of the bottom surface of the spacer layer. In this case,
since a variation in the width of the bottom surface of the spacer
layer can be kept to a lower degree, a variation in the width of
the control gate can be also kept to a lower degree. That is, a
variation in the gate length being the width of the control gate
can be kept low, thereby making it possible to improve the
manufacture yield.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The above and other purposes, advantages and features of the
present invention will become more apparent from the following
description of certain exemplary embodiments taken in conjunction
with the accompanying drawings in which:
[0024] FIG. 1 is a cross-sectional view showing a manufacturing
method of JP-A-2004-312009.
[0025] FIG. 2 is a cross-sectional view showing a manufacturing
method of JP-A-2004-312009.
[0026] FIG. 3 is a cross-sectional view showing a manufacturing
method of JP-A-2004-312009.
[0027] FIG. 4 is a cross-sectional view showing a manufacturing
method of JP-A-2004-312009.
[0028] FIG. 5 is a cross-sectional view showing a manufacturing
method of JP-A-2004-312009.
[0029] FIG. 6 is a cross-sectional view showing a manufacturing
method of JP-A-2004-312009.
[0030] FIG. 7 is a cross-sectional view showing a manufacturing
method of JP-A-2004-312009.
[0031] FIG. 8 is a cross-sectional view showing a manufacturing
method of JP-A-2004-312009.
[0032] FIG. 9 is a cross-sectional view showing a manufacturing
method of JP-A-2004-312009.
[0033] FIG. 10 is a cross-sectional view for explaining problems of
the technique of JP-A-2004-312009.
[0034] FIG. 11 is a cross-sectional view for explaining problems of
the technique of JP-A-2004-312009.
[0035] FIG. 12 is a cross-sectional view for explaining problems of
the technique of JP-A-2004-312009.
[0036] FIG. 13 is a cross-sectional view showing the configuration
of a nonvolatile semiconductor storage device according to a first
exemplary embodiment of the present invention.
[0037] FIG. 14 is a cross-sectional view showing the configuration
of a nonvolatile semiconductor storage device according to the
first exemplary embodiment of the present invention.
[0038] FIG. 15 is a cross-sectional view showing a manufacturing
method for a nonvolatile semiconductor storage device according to
the first exemplary embodiment of the present invention.
[0039] FIG. 16 is a cross-sectional view showing a manufacturing
method for a nonvolatile semiconductor storage device according to
the first exemplary embodiment of the present invention.
[0040] FIG. 17 is a cross-sectional view showing a manufacturing
method for a nonvolatile semiconductor storage device according to
the first exemplary embodiment of the present invention.
[0041] FIG. 18 is a cross-sectional view showing a manufacturing
method for a nonvolatile semiconductor storage device according to
the first exemplary embodiment of the present invention.
[0042] FIG. 19 is a cross-sectional view showing a manufacturing
method for a nonvolatile semiconductor storage device according to
the first exemplary embodiment of the present invention.
[0043] FIG. 20 is a cross-sectional view showing a manufacturing
method for a nonvolatile semiconductor storage device according to
the first exemplary embodiment of the present invention.
[0044] FIG. 21 is a cross-sectional view showing a manufacturing
method for a nonvolatile semiconductor storage device according to
the first exemplary embodiment of the present invention.
[0045] FIG. 22 is a cross-sectional view showing a manufacturing
method for a nonvolatile semiconductor storage device according to
the first exemplary embodiment of the present invention.
[0046] FIG. 23 is a cross-sectional view showing a manufacturing
method for a nonvolatile semiconductor storage device according to
the first exemplary embodiment of the present invention.
[0047] FIG. 24 is a cross-sectional view showing a manufacturing
method for a nonvolatile semiconductor storage device according to
the first exemplary embodiment of the present invention.
[0048] FIG. 25 is a cross-sectional view showing a manufacturing
method for a nonvolatile semiconductor storage device according to
the first exemplary embodiment of the present invention.
[0049] FIG. 26 is a cross-sectional view showing a manufacturing
method for a nonvolatile semiconductor storage device according to
the first exemplary embodiment of the present invention.
[0050] FIG. 27 is a cross-sectional view showing a manufacturing
method for a nonvolatile semiconductor storage device according to
the first exemplary embodiment of the present invention.
[0051] FIG. 28 is a cross-sectional view showing a manufacturing
method for a nonvolatile semiconductor storage device according to
the first exemplary embodiment of the present invention.
[0052] FIG. 29 is a cross-sectional view for explaining the
advantages of the nonvolatile semiconductor storage device and the
manufacturing method therefor according to the first exemplary
embodiment of the present invention.
[0053] FIG. 30 is a cross-sectional view showing a manufacturing
process when an upper configuration of a word gate electrode is
spread in the manufacturing method for the nonvolatile
semiconductor storage device according to the first exemplary
embodiment of the present invention.
[0054] FIG. 31 is a cross-sectional view showing a manufacturing
process when an upper configuration of a word gate electrode is
spread in the manufacturing method for the nonvolatile
semiconductor storage device according to the first exemplary
embodiment of the present invention.
[0055] FIG. 32 is a cross-sectional view showing a manufacturing
process when an upper configuration of a word gate electrode is
spread in the manufacturing method for the nonvolatile
semiconductor storage device according to the first exemplary
embodiment of the present invention.
[0056] FIG. 33 is a cross-sectional view showing a manufacturing
process when an upper configuration of a word gate electrode is
spread in the manufacturing method for the nonvolatile
semiconductor storage device according to the first exemplary
embodiment of the present invention.
[0057] FIG. 34 is a cross-sectional view showing a manufacturing
process when an upper configuration of a word gate electrode is
spread in the manufacturing method for the nonvolatile
semiconductor storage device according to the first exemplary
embodiment of the present invention.
[0058] FIG. 35 is a cross-sectional view showing the configuration
of a nonvolatile semiconductor storage device according to an
exemplary second embodiment of the present invention.
[0059] FIG. 36 is a cross-sectional view showing a manufacturing
method for the nonvolatile semiconductor storage device according
to the second exemplary embodiment of the present invention.
[0060] FIG. 37 is a cross-sectional view showing a manufacturing
method for the nonvolatile semiconductor storage device according
to the second exemplary embodiment of the present invention.
[0061] FIG. 38 is a cross-sectional view showing a manufacturing
method for the nonvolatile semiconductor storage device according
to the second exemplary embodiment of the present invention.
[0062] FIG. 39 is a cross-sectional view showing a manufacturing
method for the nonvolatile semiconductor storage device according
to the second exemplary embodiment of the present invention.
[0063] FIG. 40 is a cross-sectional view showing a manufacturing
method for the nonvolatile semiconductor storage device according
to the second exemplary embodiment of the present invention.
[0064] FIG. 41 is a cross-sectional view showing a manufacturing
method for the nonvolatile semiconductor storage device according
to the second exemplary embodiment of the present invention.
[0065] FIG. 42 is a cross-sectional view showing a manufacturing
method for the nonvolatile semiconductor storage device according
to the second exemplary embodiment of the present invention.
[0066] FIG. 43 is a cross-sectional view showing a manufacturing
method for the nonvolatile semiconductor storage device according
to the second exemplary embodiment of the present invention.
[0067] FIG. 44 is a cross-sectional view showing a manufacturing
method for the nonvolatile semiconductor storage device according
to the second exemplary embodiment of the present invention.
[0068] FIG. 45 is a cross-sectional view showing the configuration
of a nonvolatile semiconductor storage device according to a third
exemplary embodiment of the present invention.
[0069] FIG. 46 is a cross-sectional view showing the respective
processes in the manufacturing method for the nonvolatile
semiconductor storage device according to the third exemplary
embodiment of the present invention.
[0070] FIG. 47 is a cross-sectional view showing the respective
processes in the manufacturing method for the nonvolatile
semiconductor storage device according to the third exemplary
embodiment of the present invention.
[0071] FIG. 48 is a cross-sectional view showing the respective
processes in the manufacturing method for the nonvolatile
semiconductor storage device according to the third exemplary
embodiment of the present invention.
[0072] FIG. 49 is a cross-sectional view showing the respective
processes in the manufacturing method for the nonvolatile
semiconductor storage device according to the third exemplary
embodiment of the present invention.
[0073] FIG. 50 is a cross-sectional view showing the respective
processes in the manufacturing method for the nonvolatile
semiconductor storage device according to the third exemplary
embodiment of the present invention.
[0074] FIG. 51 is a cross-sectional view showing the respective
processes in the manufacturing method for the nonvolatile
semiconductor storage device according to the third exemplary
embodiment of the present invention.
[0075] FIG. 52 is a cross-sectional view showing the respective
processes in the manufacturing method for the nonvolatile
semiconductor storage device according to the third exemplary
embodiment of the present invention.
[0076] FIG. 53 is a cross-sectional view showing the respective
processes in the manufacturing method for the nonvolatile
semiconductor storage device according to the third exemplary
embodiment of the present invention.
[0077] FIG. 54 is a cross-section view showing a modification of
the exemplary second embodiment.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0078] The invention will now be described herein with reference to
illustrative exemplary embodiments. Those skilled in the art will
recognize that many alternative embodiments can be accomplished
using the knowledge of the present invention and that the invention
is not limited to the exemplary embodiments illustrated for
explanatory purposes.
First Exemplary Embodiment
[0079] First, a description will be given of the configuration of a
nonvolatile semiconductor storage device according to the first
exemplary embodiment of the present invention. FIG. 13 is a
cross-sectional view showing the configuration of the nonvolatile
semiconductor storage device according to the first exemplary
embodiment of the present invention. The figure exemplifies a flash
memory cell with a TWIN-MONOS structure as a memory cell 2 of the
nonvolatile semiconductor storage device according to the first
exemplary embodiment.
[0080] The memory cell 2 includes a word gate electrode 20, a word
gate insulating film 15, a control gate electrode 30, an Oxide
Nitride Oxide film: oxide-nitride-oxide (ONO) film 11, a spacer 17,
a side wall insulating film 16, a source/drain diffusion layer 51,
and silicide layers 61, 62.
[0081] The word gate electrode-20 is formed on a channel region (a
surface region of the semiconductor substrate 10) through the word
gate insulating film 15. The word gate electrode 20 is exemplified
by polysilicon doped with impurities. A height of the word gate
electrode 20 from the surface of the semiconductor substrate 10 is
higher than a height of the control gate electrode 30 from the
surface of the semiconductor substrate 10. As a result, when the
silicide layer 62 (which will be described later) is formed on the
word gate electrode 20, there is no risk that a layer that
short-circuits the word gate electrode 20 and the control gate
electrode 30 is formed. The word gate electrode 20 may have a top
surface side larger in width than a bottom surface side as will be
described later. In such a case, since an area of the silicide
layer 62 can be widened, the configuration can contribute to low
resistance of the silicide layer 62. The silicide layer 62 is
formed on an upper portion of the word gate electrode 20. The
silicide layer 62 is exemplified by a cobalt silicide.
[0082] The word gate insulating film 15 is formed on the channel
region sandwiched between the source/drain diffusion layers 51 so
as to cover a bottom surface and both side surfaces of the word
gate electrode 20. The word gate insulating film 15 is exemplified
by silicon oxide. The word gate insulating film 15 has no function
of storing electric charges. That is, no electric charges are
stored on the bottom surface and the side surfaces of the word gate
electrode 20. No ONO film 11 (charge storage layer: described
later) is located at the side surfaces of the word gate electrode
20. Instead, the word gate insulating film 15 covers the side
surfaces of the word gate electrode 20, thereby making it possible
to set a charge storage region to only the ONO film 11 below the
control gate electrode 30. As a result, electric charges can
locally exist in only the ONO film 11 facing the channel region,
thereby increasing the reliability of the operation.
[0083] The control gate electrodes 30 are formed on both side
surfaces of the word gate electrode 20 through the word gate
insulating film 15, and on the channel region through the ONO films
11. The control gate electrodes 30 are exemplified by polysilicon
doped with impurities. The top surfaces of the control gate
electrodes 30 are substantially parallel to the flat surface of the
semiconductor substrate 10, and are substantially flat. In the
TWIN-MONOS structure shown in FIG. 13, one memory cell 2 has the
two control gate electrodes 30 on both sides of one word gate
electrode 20.
[0084] Each of the ONO films 11 is a charge storage layer, and
formed between the control gate electrode 30 and the channel
region. The ONO film 11 may have a three-layer structure including
of an oxide film 12, a nitride film 13, and an oxide film 14, which
are exemplified by a silicon oxide film, a silicon nitride film,
and a silicon oxide film, respectively. As described above, since
the ONO film 11 is formed only in a region facing the channel
region, the stored charges cannot escape to another region. As a
result, it is possible to appropriately transfer electric charges
by aid of the control gate electrodes 30 and the word gate
electrodes 20.
[0085] Each of the spacers 17 is formed on the control gate
electrode 30. The spacer layer 17 is exemplified by a silicon
nitride film. A height of a top surface 17f of the spacer layer 17
from a bottom surface 17b is lower as the top surface 17f is
farther from the word gate electrode 20. Also, a width of the
spacer layer 17 is narrower as the spacer layer 17 is farther from
the control gate electrode 30. A width of the bottom surface 17b of
the spacer layer 17 coincides with a width of a top surface 30t of
the control gate electrode 30, and the width of the bottom surface
17b of the spacer layer 17 corresponds to a gate length of the
control gate electrode 30. Also, a side surface 17h of the spacer
layer 17 at an opposite side of the word gate electrode 20 side is
included in a flat surface P or located at the word gate electrode
20 side with respect to the flat surface P on which a side surface
30h of the control gate electrode 30 at an opposite side of the
word gate electrode 20 side extends in a direction apart from the
surface of the semiconductor substrate 10. That is, the side
surface 17h has no inverse taper shown in FIG. 12.
[0086] Each of the side wall insulating films 16 is formed so as to
cover side surfaces of the control gate electrode 30, the ONO film
11, and the spacer layer 17 at an opposite side of the word gate
electrode 20 side. The side wall insulating film 16 is exemplified
by a unilaminate silicon oxide film, or a laminate structure
including a silicon oxide film, a silicon nitride film, and a
silicon oxide film. The respective gate electrodes 30 of the
adjacent memory cells 2 are each surrounded by the side wall
insulating film 16, and an interlayer insulating layer 19, so as to
be insulated from each other.
[0087] The source/drain fusion layers 51 are formed at both sides
of the channel region on the surface of the semiconductor substrate
10. Each of the source/drain diffusion layers 51 includes a
low-concentration diffusion layer (LDD diffusion layer) 51a and a
high-concentration diffusion layer 51b. Each of the
low-concentration diffusion layers 51a is formed at a position
substantially immediately below the side wall insulating film 16 so
as to project from the source/drain diffusion layer 51 to the
channel region. The impurities are exemplified by arsenic (As) or
phosphorous (P) in the case of n-type conductivity, and exemplified
by boron (B) in the case of p-type conductivity. Each of the
silicide layers 61 is formed on an upper portion of the
source/drain diffusion layer 51. The silicide layer 61 is
exemplified by cobalt silicide. An upper portion of each silicide
layer 61 is connected with a contact 71, which is further connected
to a wiring 72 being an upper layer (exemplification: bit line) In
the present invention, each of the spacer layers 17 becomes lower
as it extends farther from the word gate electrode 20. In this
case, when the flat surface P substantially perpendicular to the
surface of the semiconductor substrate 10 (and a polysilicon film
20a) extends so as to include a line of intersection of the bottom
surface 17b and the side surface 17h, the side surface 17h is
included in the flat surface P substantially perpendicular to the
side surface, or is inclined toward the word gate electrode 20
side.
[0088] In other words, the side surface 17h is not inclined toward
a side apart from the word gate electrode 20 with respect to the
substantially perpendicular flat surface P. That is, the side
surface 17h has no inverse taper shown in FIG. 12. As will be
described later, the control gate electrode 30 obtained by etching
with the above spacer layer 17 as a mask has the same width as that
of the bottom surface 17b of the spacer layer 17. That is, the
width of the bottom surface 17b of the spacer layer 17 can be made
to correspond directly to the gate length of the control gate
electrode 30. In this example, since the degree of a variation in
the width of the bottom surface 17b of the spacer layer 17 can be
kept low, a variation in the gate length of the control gate
electrode 30 is suppressed so as to appropriately execute control,
thereby making it possible to improve the manufacture yield.
[0089] FIG. 14 is a plan view showing the configuration of a
nonvolatile semiconductor storage device according to the first
exemplary embodiment. In FIG. 14, the silicide layers 61, 62, the
interlayer insulating layer 19, and the wiring 72 are omitted.
[0090] In the nonvolatile semiconductor storage device, plural
memory cells 2 (a region surrounded by a broken line) are aligned
in a matrix. A word gate electrode 20 extends in an X-direction,
and is shared by the plural memory cells 2 aligned in the
x-direction. The control gate electrodes 30 extend along both sides
of the word gate electrode 20 through the word gate insulating
films 15 in the X-direction, and are shared by the plural memory
cells aligned in the X-direction. The word gate electrode 20 and
the control gate electrodes 30 also function as wirings.
[0091] Also, on the surface of the semiconductor substrate 10 are
formed plural device isolation regions 8 that electrically isolate
the surface regions from each other, and extend in a Y-direction.
The memory cell 2 is a region that is sandwiched between the device
isolation regions 8, and includes one word gate electrode 20, the
control gate electrodes at both sides of the word gate electrode
20, and regions close to the control gate electrodes 30
(source/drain diffusion layer 51). For example, the memory cell 2
is a region surrounded by a square frame (broken line) in FIG. 14.
The memory cell 2 shown in FIG. 13 corresponds to a cross section
taken along a line A-A' in FIG. 14. The contact 71 connects the
source/drain diffusion layer 51 of the memory cell 2 to a wiring
(not shown, exemplification: bit line) arranged on the upper
layer.
[0092] Subsequently, a description will be given of the operation
of the nonvolatile semiconductor storage device according to the
first exemplary embodiment with reference to FIG. 13. First, the
operation of writing information in the memory cell 2 will be
described. A positive potential of about 1 V is applied to the word
gate electrode 20, a positive potential of about 6 V is applied to
the control gate electrode 30 at a writing side (hereinafter
referred to as a "select side"), a positive potential of about 3 V
is applied to the control gate electrode 30 at a non-writing side
(hereinafter referred to as an "unselect side") paired with the
control gate electrode 30, a positive potential of about 5 V is
applied to the source/drain diffusion layer 51 at the select side,
and about 0 V is applied to the source/drain diffusion layer 51 at
the unselect side. As a result, hot electrons that have occurred in
the channel region are implanted into the nitride film 13 of the
ONO film 11 at the select side. This is called "Channel Hot
Electron (CHE) implantation". As a result, data is written.
[0093] Subsequently, a description will be given of the operation
of erasing information written in the memory cell 2. About 0 V is
applied to the word gate electrode 20, a negative potential of
about -3 V is applied to the control gate electrode 30 at the
writing side, a positive potential of about 2 V is applied to the
control gate electrode 30 at the non-writing side, and a positive
potential of about 5 V is applied to the source/drain diffusion
layer 51 at the select side. As a result, a hole electron pair
occurs due to an inter-band tunnelling, and the holes or holes
having occurred by colliding with those holes, are accelerated to
provide hot holes which are implanted into the nitride film 14 of
the ONO film 11 at the select side. As a result, negative charges
that have been charged in the nitride film of the ONO film 11 are
canceled to erase data.
[0094] Subsequently, a description will be given of the operation
of reading information written in the memory cell 2. A positive
potential of about 2 V is applied to the word gate electrode 20, a
positive potential of about 2 V is applied to the control gate
electrode 30 at the select side, a positive potential of about 3 V
is applied to the control gate electrode 30 at the unselect side,
about 0 V is applied to the source/drain diffusion layer 51 at the
select side, and about 1.5V is applied to the source/drain
diffusion layer 51 at the unselect side. In that state, a threshold
value of the memory cell 2 is detected. When negative electric
charges are stored in the ONO film 11 at the select side, the
threshold value is increased to more than that in the case where
the negative electric charges are not stored. Therefore, the
threshold value is detected, thereby making it possible to read
information read in the ONO film 11 at the select side. In the
memory cell 2 shown in FIG. 13, information of two bits where one
bit is provided at each side of the word gate electrode 20 can be
recorded.
[0095] Subsequently, a description will be given of a method of
manufacturing the nonvolatile semiconductor storage device
according to the first exemplary embodiment. FIGS. 15 to 28 are
cross-sectional views showing respective processes in the method of
manufacturing the nonvolatile semiconductor storage device
according to the first exemplary embodiment. FIGS. 15 to 28
correspond to a cross section taken along a line A-A' in FIG. 14.
Hereinafter, a description will be given of an example in which the
word gate electrode 20 and the control gate electrodes 30 are each
formed of a polysilicon film.
[0096] As shown in FIG. 15, on the surface of the semiconductor
substrate 10 made of the p-type silicon are laminated a silicon
oxide film as the oxide film 12, a silicon nitride film as the
nitride film 13, and a silicon oxide film as the oxide film 14 in
the stated order. The first silicon oxide film 12 is formed in, for
example, a thickness of about 3 to 5 nm through a wetoxidizing
method or a radical oxidizing method. The silicon nitride film 13
is formed in, for example, a thickness of about 6 to 10 nm through
a chemical vapor deposition (CVD) method. The last silicon oxide
film 14 is formed in, for example, a thickness of about 3 to 10 nm
through the radical oxidizing, the wet oxidizing or CVD method. As
a result, the ONO film 11 functioning as the charge storage layer
is formed. Thereafter, a polysilicon film 30a is formed so as to
cover the ONO film 11 through the CVD method. The polysilicon film
30a is formed in, for example, a thickness of about 50 to 200 nm,
and doped with In-Situ contained in the film or doped with
impurities by ion implantation after the film has been formed. The
polysilicon film 30a forms the control gate electrodes 30 in a
post-process. Then, a silicon nitride film is formed as a mask film
80 through the CVD method so as to cover the polysilicon film 30a.
The mask film 80 is formed in, for example, a thickness of about 50
to 200 nm.
[0097] Then, as shown in FIG. 16, a photo resist (not shown) having
a pattern of the word gate electrode 20 is formed through a
photolithography technique. Then, the mask film 80, the polysilicon
film 30a, and the ONO film 11 are sequentially dry-etched with the
photo resist as a mask to form a trench 81. The word gate electrode
20 is formed within the trench 81 in a post-process. Thereafter,
the photo resist is removed.
[0098] Subsequently, as shown in FIG. 17, the word gate insulating
film 15 (silicon oxide) is formed through the CVD method so as to
cover the inside of the mask film 80 and the trench 81. The word
gate insulating film 15 is formed in, for example, a thickness of
about 10 to 30 nm. A width of the trench 81 after the word gate
insulating film 15 has been formed corresponds to a gate length of
the word gate electrode 20. For example, the width is about 60 to
200 nm. Then, the polysilicon film 20a is formed through the CVD
method so as to cover the word gate insulating film 15 and fill in
the trench 81. The polysilicon film 20a is formed in, for example,
a thickness of about 60 to 200 nm, and then doped with In-Situ
impurities contained in the film or doped with impurities by ion
implantation after the film has been formed. The polysilicon film
20a forms the word gate electrodes 20 in a post-process.
[0099] Then, as shown in FIG. 18, the polysilicon film 20a and the
word gate insulating film 15 are removed and planarized through
etch back or chemical mechanical polishing (CMP) so as to be
adjusted to the height of the mask film 80 (remain only within the
trench 81). As a result, the polysilicon film 20a forms the word
gate electrode 20. Subsequently, as shown in FIG. 19, the upper
portion of the word gate electrode 20 is thermally oxidized to form
the oxide film 82 in, for example, a thickness of about 10 to 50
nm. Thereafter, as shown in FIG. 20, the mask film 80 is removed by
etching. As a result, the upper portion of the word gate electrode
20 whose sides are covered with the word gate insulating film 15
and whose top surface is covered with the oxide film 82 projects
from the surface of the polysilicon film 30a.
[0100] Subsequently, as shown in FIG. 21, a silicon nitride film is
formed as a spacer film 17a in, for example, a thickness of about
30 to 100 nm through the CVD method so as to cover the word gate
electrode 20 covered with the word gate insulating film 15 and the
nitride film 82, and the polysilicon film 30a. Thereafter, as shown
in FIG. 22, the spacer film 17a is etched back. As a result, a
spacer 17 is formed on the side surface of the word gate electrode
20 through the word gate insulating film 15, and on the surface of
the polysilicon film 30a. Then, as shown in FIG. 23, the
polysilicon film 30a and the ONO film 11 are sequentially etched
with the spacer layer 17 as a mask. As a result, the control gate
electrode 30 is formed. The surface of the semiconductor substrate
10 is exposed outside of the control gate electrode 30. At this
time, a width of the spacer layer 17 becomes a gate length of the
control gate electrode 30.
[0101] Subsequently, as shown in FIG. 24, impurities are implanted
into the surface region of the semiconductor substrate 10 with the
spacer layer 17, the word gate electrode 20, and the word gate
insulating film 15 acting as a mask, to form a low-concentration
diffusion layer 51a. Then, as shown in FIG. 25, a silicon oxide
film is formed on the entire surface in a thickness of about 10 to
20 nm through the CVD method, and etched back to form a side wall
insulating film 16 on the side surfaces of the spacer layer 17, the
control gate electrode 30, and the ONO film 11. Thereafter, as
shown in FIG. 26, impurities are implanted into the surface region
of the semiconductor substrate 10 with the side wall insulating
film 16, the spacer layer 17, the word gate electrode 20, and the
word gate insulating film 15 as a mask, to form a
high-concentration diffusion layer 51b. The low-concentration
diffusion layer 51a and the high-concentration diffusion layer 51b
constitute the source/drain diffusion layer 51.
[0102] Then, as shown in FIG. 27, a metal film exemplified by
cobalt is formed in about 10 nm thickness on the entire surface
through the sputtering method to form the silicide layers 62 and 61
on the word gate electrode 20 and the source/drain diffusion layer
51 through a given heat treatment, respectively. Then, as shown in
FIG. 28, after the formation of the interlayer insulating layer 19
on the entire surface, the contact 71 that penetrates the
interlayer insulating layer 19 is formed on the source/drain
diffusion layer to form a wiring 72 on the contact 71.
[0103] With the above operation, the nonvolatile semiconductor
storage device (FIG. 13) according to the first exemplary
embodiment is manufactured.
[0104] FIG. 29 is a cross-sectional view for explaining the
advantages of the nonvolatile semiconductor storage device and the
manufacturing method therefor according to this embedment. FIG. 29
shows the polysilicon film in processes of FIGS. 22 to 23.
[0105] The spacer layer 17 is formed by etch back in a process of
FIG. 22. Accordingly, in a height of a top surface 17t from a
bottom surface 17b of the spacer layer 17 (a surface 30t of the
polysilicon film 30a), a height L13 at a side surface 17h at an
opposite side of the word gate electrode 20 is lower than a height
L14 at a side surface 17k at the word gate electrode 20 side. That
is, the height L13 is lower as the side surface 17h is (e.g.,
extends) farther from the word gate electrode 20. In this
situation, when a flat surface substantially perpendicular to the
surface of the semiconductor substrate 10 (and the polysilicon film
30a) extends so as to include a line of intersection of the bottom
surface 17b and the side surface 17h, the side surface 17h is
included in the flat surface substantially perpendicular to the
side surface, or inclined toward the word gate electrode 20 side.
Accordingly, the side surface 17h is not inclined toward a side
apart from the word gate electrode 20 with respect to the
substantially perpendicular flat surface. That is, the side surface
17h has no inverse taper shown in FIG. 12.
[0106] When the polysilicon film 30a is etched with the above
spacer layer 17 as a mask, since no inverse taper exists, the
polysilicon film 30a is etched by the width of the bottom surface
17b of the spacer layer 17. As a result, it is possible that a
width L12 of the bottom surface 17b of the spacer layer 17 is made
to coincide with a width L15 of the top surface 30t of the control
gate electrode 30. That is, the width L12 of the bottom surface 17b
of the spacer layer 17 can be made to correspond directly to the
gate length of the control gate electrode 30. In this case, since
the degree of a variation in the width L12 of the bottom surface
17b of the spacer layer 17 can be also kept low, a variation in the
gate length of the control gate electrode 30 can be also kept low.
That is, it is possible to improve the manufacture yield.
[0107] The manufacturing method for the nonvolatile semiconductor
storage device according to the first exemplary embodiment is
clearly different from the manufacturing method disclosed in
JP-A-2004-312009 as shown in FIGS. 15 to 28. For that reason, the
spacer layer 17 in the first exemplary embodiment is not inversely
tapered as shown in FIG. 12, and the above advantage can be
obtained. However, in the manufacturing method for the nonvolatile
semiconductor storage device according to the first exemplary
embodiment, there is the possibility that the upper configurations
of the word gate electrode 20 and the gate insulating film 15 are
spread outward as shown in FIG. 29. However, an influence of the
spread configuration on the top surface 17t and the side surface
17h of the spacer layer 17 is extremely small, and there arises no
problem in the above effect. The reason will be described
below.
[0108] FIGS. 30 to 34 are cross-sectional views showing a
manufacturing process when the upper configuration of the word gate
electrode 20 is spread in the manufacturing method for the
nonvolatile semiconductor storage device according to the first
exemplary embodiment. FIGS. 30 to 34 correspond to FIGS. 16, 20,
21, the mid-flow of FIGS. 21 and 22, and FIG. 22.
[0109] As shown in FIG. 30, the mask film 80 has a side surface 80h
liable to be tapered in etching for forming the trench 81 in FIG.
16. That is, a portion of the side surface 80h at the top surface
side is configured to be recessed toward the mask film 80 side with
respect to a portion thereof at the side of the semiconductor
substrate 10 by .DELTA.11. In that case, as shown in FIG. 31, the
word gate electrode 20 and the word gate insulating film 15 are
configured so that their upper portion confirmations are spread
outward in a stage of FIG. 20. As a result, an upper side wall 15h
of the word gate insulating film 15 is inversely tapered. That is,
a portion of the side wall 15h at the side of the semiconductor
substrate 10 is configured to be recessed toward the word gate
electrode 20 side by .DELTA.12 (substantially equal to .DELTA.11)
with respect to a portion thereof at the top surface side. In this
case, it is assumed that a height of the inversely tapered portion
of the side wall 15h is L10.
[0110] In the above state, when the spacer film 17a is formed so as
to cover the word gate electrode 20 and the polysilicon film 30a in
a process of FIG. 21, the spacer film 17a has its upper
configuration spread outward along the configurations of the word
gate electrode 20 and the word gate insulating film 15, as shown in
FIG. 32. As a result, an upper side wall 17ah of the spacer film
17a is inversely tapered. That is, a portion of the side wall 17ah
at the side of the semiconductor substrate 10 is configured to be
recessed toward the word gate electrode 20 side by .DELTA.13 with
respect to a portion at the top surface side. However, a recess 90
being an inversely tapered portion is of no configuration tracing
the configuration of the upper side wall 15h of the word gate
insulating film 15 as it is, but of a slightly dulled configuration
so as to be reduced more than L10 by the thickness of the spacer
layer 17a. That is, when it is assumed that a height of an
inversely tapered portion of the side wall 17ah is L10A,
L10A<L10 as well as .DELTA.13<.DELTA.12 is satisfied. In this
way, the formation of the spacer film 17a whose configuration of
the outer surface is free enables an influence of the inverse taper
to be suppressed.
[0111] Besides, in this state, when the spacer film 17a is etched
back in a process of FIG. 21, the spacer film 17a is etched by
etching ions that are input substantially perpendicularly to the
surface of the semiconductor substrate 10, as shown in FIG. 33. In
this situation, the spacer film 17a is etched in the substantially
perpendicular direction with the substantially same thickness over
the entire surface of the semiconductor substrate 10. As shown in
FIG. 33, the spacer film 17a initially having a configuration
indicated by a broken line is etched in the substantially
perpendicular direction with the substantially same thickness over
the entire surface into a configuration indicated by a solid line.
In this situation, a recess 90A of the inverse taper is reduced
smaller than the recess 90, and a height L10B of the inversely
tapered portion is also smaller than the height L10A. Then, when
the height L10A of the inversely tapered portion during the initial
phase of etch back is smaller than the etch back quantity of the
spacer film 17a, the inversely tapered portion at the side wall 17h
can be eliminated finally as shown in FIG. 34. Even if the height
L10A of the inversely tapered portion during the initial phase of
etch back is larger than the etch back quantity of the spacer film
17a, it is possible to further reduce the size of the recess 90A,
and the height of the inversely tapered portion can be further
reduced more than L10A. As a result, it is possible to remarkably
suppress an influence of the inverse taper.
[0112] In this way, since the inversely tapered portion is finally
eliminated or remarkably reduced, it is possible to substantially
ignore the inversely tapered portion with respect to the intended
spacer layer 17. Accordingly, even if the spacer layer 17 is used
as an etching mask of the polysilicon film 30a, it is conceivable
that etching is hardly affected by the inverse taper of the word
gate electrode 20. That is, when the polysilicon film 30a is
etched, etching ions reach the polysilicon film 30a while their
courses are restricted by the top surface 17t and the side wall 17h
of the spacer layer 17. In this situation, because the inversely
tapered portion hardly exists, there is no case in which etching
ions go round to that portion. Accordingly, it is possible to etch
the polysilicon film 30a with a width predetermined by the top
surface 17t and the sidewall 17h. Accordingly, it is possible to
form the control gate electrode 30 with the width predetermined by
the top surface 17t and the side wall 17h.
[0113] Also, even if the inversely tapered portion remains, and
etching ions go around to that portion for etching, because a width
of that portion is extremely small, its influence is similarly
extremely small, and the control gate electrode 30 can be formed
with a width that is rarely different from the width predetermined
by the top surface 17t and the side wall 17h. Further, there is a
risk that etching ions do not go around to the inversely tapered
portion, or go around thereto, thereby causing the width of the
control gate electrode 30 to be varied. However, as described
above, because the height of the inversely tapered portion is
smaller than L10A (than L10), the control gate electrode 30 can be
formed with a width that is rarely different from the width
predetermined by the top surface 17t and the side wall 17h
regardless of the presence or degree of go-around of etching ions.
Accordingly, there arises no problem on a variation in the width of
the control gate electrode 30.
[0114] As described above, in the present invention, the height of
the inversely tapered portion can be more surely decreased as
compared with the case of JP-A-2004-312009. Further, the film
thickness of the spacer layer 17a, the height (=L10) of the mask
film 80, and the etch back quality are appropriately set, thereby
enabling the occurrence of the inversely tapered portion to be
finally removed.
[0115] Also, in the technique of JP-A-2004-312009, in order to form
the control gate electrode 130, it is necessary to execute
selective etching by the aid of at least three kinds of insulating
films that can provide etching selectivity as the buffer layer 180,
the first insulating spacer 117, and the gate dielectric layer 115
in the processes of FIGS. 6 and 7. However, it is difficult to
select the above insulating films in a normal silicon process.
However, in the first exemplary embodiment, in order to form the
control gate electrode 30, for example, it is possible to execute
selective etching by the aid of two kinds of insulating films that
can provide etching selectivity, such as the oxide film 82 on the
word gate electrode 20, the word gate insulating film 15 (silicon
oxide), and the spacer layer 17 (silicon oxide) in the processes of
FIGS. 22 and 23. That is, the first exemplary embodiment can be
readily realized in a normal silicon process.
Second Exemplary Embodiment
[0116] First, a description will be given of the configuration of
the nonvolatile semiconductor storage device according to the
second exemplary embodiment of the present invention. FIG. 35 is a
cross-sectional view showing the configuration of the nonvolatile
semiconductor storage device according to the second exemplary
embodiment of the present invention. FIG. 35 exemplifies a flash
memory cell with a MONOS structure as a memory cell 2a of the
nonvolatile semiconductor storage device according to the second
exemplary embodiment.
[0117] The memory cell 2a differs from that in the first exemplary
embodiment in that the control gate electrode 30 has a two-layer
structure (polycide structure) including of the control gate layer
31 and the silicide layer 32. That is, the control gate electrode
30 is formed on both side surfaces of the word gate electrode 20
through the word gate insulating film 15, and on the channel region
through the ONO film 111. The control gate electrode 30 includes
the control gate layer 31 being a lower layer disposed on the ONO
film 11, and the silicide layer 32 disposed between the control
gate layer 31 and the spacer layer 17. The control gate layer 31 is
exemplified by polysilicon doped with impurities, and the silicide
layer 32 is exemplified by tungsten silicide. The top surface of
the control gate layer 31 is substantially parallel to the flat
surface of the semiconductor substrate 10, and flat. In the
TWIN-MONOS structure shown in FIG. 35, each of the memory cells 2
has two control gate electrodes 30 at both sides of one word gate
electrode 20.
[0118] Other configurations (including FIG. 14) and operation are
identical with those in the first exemplary embodiment, and
therefore their description will be omitted.
[0119] Subsequently, a description will be given of a method of
manufacturing the nonvolatile semiconductor storage device
according to the second exemplary embodiment. FIGS. 36 to 44 are
cross-sectional views showing respective processes in the method of
manufacturing the nonvolatile semiconductor storage device
according to the second exemplary embodiment. FIGS. 36 to 44
correspond to a cross section taken along a line A-A' in FIG. 14.
Hereinafter, a description will be given of an example in which the
word gate electrode 20 is formed of a polysilicon film and the
control gate electrodes 30 are formed of a polysilicon film and a
tungsten silicide film, respectively.
[0120] As shown in FIG. 36, on the surface of the semiconductor
substrate 10 made of the p-type silicon are laminated a silicon
oxide film as the oxide film 12, a silicon nitride film as the
nitride film 13, and a silicon oxide film as the oxide film 14 in
the stated order. The first silicon oxide film is formed in, for
example, a thickness of about 3 to 5 nm through a wet oxidizing
method or a radical oxidizing method. The silicon nitride film is
formed in, for example, a thickness of about 6 to 10 nm through a
CVD method. The last siliconoxide film is formed in, for example, a
thickness of about 3 to 10 nm through the radical oxidizing, the
wet oxidizing or CVD method. As a result, the ONO film 11
functioning as the charge storage layer is formed. Thereafter, the
polysilicon film 30a is formed so as to cover the ONO film 11
through the CVD method. The polysilicon film 31a is formed in, for
example, a thickness of about 25 to 100 nm, and doped with In-Situ
impurities contained in the film or doped with impurities by ion
implantation after the film has been formed. The polysilicon film
30a forms the control gate electrodes 31 in a post-process. Then, a
tungsten silicide film 32a is formed through the CVD method so as
to cover the polysilicon film 31a. The tungsten silicide film 32a
is formed in, for example, a thickness of about 25 to 100 nm. The
tungsten silicide film 32a forms the silicide layer 32 in a
post-process. Thereafter, the silicon nitride film is formed as the
mask film 80 so as to cover the tungsten silicide film 32a. The
mask film 80 is formed in, for example, a thickness of about 50 to
200 nm.
[0121] Then, as shown in FIG. 37, a photo resist (not shown) having
a pattern of the word gate electrode 20 is formed through a
photolithography technique. Then, the mask film 80, the tungsten
silicide film 32a, the polysilicon film 31a, and the ONO film 11
are sequentially dry-etched with the photo resist as a mask to form
the trench 81. The word gate electrode 20 is formed within the
trench 81 in a post-process. Thereafter, the photo resist is
removed.
[0122] Subsequently, as shown in FIG. 38, the word gate insulating
film 15 is formed through the CVD method so as to cover the inside
of the mask film 80 and the trench 81. The word gate insulating
film 15 is formed in, for example, 10 to 30 nm. A width of the
trench 81 after the word gate insulating film 15 has been formed
corresponds to a gate length of the word gate electrode 20. For
example, the width is about 60 to 200 nm. Then, the polysilicon
film 20a is formed through the CVD method so as to cover the word
gate insulating film 15 and fill in the trench 81. The polysilicon
film 20a is formed in, for example, a thickness of about 60 to 200
nm, and then doped with In-Situ impurities contained in the film or
doped with impurities by ion implantation after the film has been
formed. The polysilicon film 20a forms the word gate electrodes 20
in a post-process.
[0123] Then, as shown in FIG. 39, the polysilicon film 20a and the
word gate insulating film 15 are removed and planarized through
etch back or CMP so as to be adjusted to the height of the mask
film 80 (remain only within the trench 81). As a result, the
polysilicon film 20a forms the word gate electrode 20.
Subsequently, as shown in FIG. 40, the upper portion of the word
gate electrode 20 is thermally oxidized to form the oxide film 82
in, for example, a thickness of about 10 to 50 nm. Thereafter, as
shown in FIG. 41, the mask film 80 is removed by etching. As a
result, the upper portion of the word gate electrode 20 whose sides
are covered with the word gate insulating film 15 and whose top
surface is covered with the oxide film 82 projects from the surface
of the tungsten silicide film 32a.
[0124] Subsequently, as shown in FIG. 42, a silicon nitride film is
formed as a spacer film 17a in, for example, a thickness of about
30 to 100 nm through the CVD method so as to cover the word gate
electrode 20 covered with the word gate insulating film 15 and the
nitride film 82, and the polysilicon film 30a. Thereafter, as shown
in FIG. 43, the spacer film 17a is etched back. As a result, a
spacer 17 is formed on the side surface of the word gate electrode
20 through the word gate insulating film 15, and on the surface of
the tungsten silicide film 32a. Then, as shown in FIG. 44, the
tungsten silicide film 32a, the polysilicon film 31a, and the ONO
film 11 are sequentially etched with the spacer layer 17 as a mask.
As a result, the control gate electrode 30 (the control gate layer
31 and the silicide layer 32) is formed. The surface of the
semiconductor substrate 10 is exposed outside of the control gate
electrode 30. At this time, a width of the spacer layer 17 becomes
a gate length of the control gate electrode 30.
[0125] The subsequent processes are identical with those in FIGS.
24 to 28 in the first exemplary embodiment, and therefore their
description will be omitted. With the above operation, the
nonvolatile semiconductor storage device (FIG. 35) according to the
second exemplary embodiment is manufactured.
[0126] Similarly, in the second exemplary embodiment, the same
advantages as those in the first exemplary embodiment can be
obtained. Also, in the second exemplary embodiment, the control
gate electrode 30 has a two-layer structure (the polycide structure
of polysilicon and silicide) including the control gate layer 31
and the silicide layer 32. For that reason, the control gate
electrode 30 can be reduced in resistance, thereby enabling
high-speed operation to be realized.
Third Exemplary Embodiment
[0127] First, a description will be given of the configuration of a
nonvolatile semiconductor storage device according to a third
exemplary embodiment of the present invention. FIG. 45 is a
cross-sectional view showing the configuration of the nonvolatile
semiconductor storage device according to the third exemplary
embodiment of the present invention. FIG. 45 exemplifies a flash
memory cell with a MONOS structure as a memory cell 2b of the
nonvolatile semiconductor storage device according to the third
exemplary embodiment.
[0128] The memory cell 2b differs from that in the first exemplary
embodiment in that the control gate electrode 30 is disposed at
only one side of the word gate electrode 20. Other configurations
(including FIG. 14) and operation are identical with those in the
first exemplary embodiment, and therefore their description will be
omitted.
[0129] Subsequently, a description will be given of a method of
manufacturing the nonvolatile semiconductor storage device
according to the third exemplary embodiment. FIGS. 46 to 53 are
cross-sectional views showing respective processes in the method of
manufacturing the nonvolatile semiconductor storage device
according to the third exemplary embodiment. FIGS. 46 to 53
correspond to a cross section taken along a line A-A' in FIG. 14.
Hereinafter, a description will be given of an example in which the
word gate electrode 20 and the control gate electrode 30 are formed
of a polysilicon film.
[0130] Initial processes of the manufacturing method for the
nonvolatile semiconductor storage device according to the third
exemplary embodiment are identical with the processes in FIGS. 15
to 22 in the first exemplary embodiment, and therefore their
description will be omitted. The results of those processes become
a state shown in FIG. 46 (as in FIG. 22).
[0131] Then, as shown in FIG. 47, a photo resist 88 covering only
one side of the word gate electrode 20 is formed through a
photolithography technique. Then, the spacer layer 17 at one side
of the word gate electrode 20 is removed with the photo resist 88
as a mask. Thereafter, the photo resist 88 is removed.
[0132] Subsequently, as shown in FIG. 48, the polysilicon film 30a
and the ONO film 11 are sequentially etched with the spacer layer
17 as a mask. As a result, the control gate electrode 30 is formed
at one side of the word gate electrode 20. The surface of the
semiconductor substrate 10 is exposed to the outside of the control
gate electrode 30 and one side of the word gate electrode 20. In
this case, the width of the spacer layer 17 becomes the gate length
of the control gate electrode 30.
[0133] Then, as shown in FIG. 49, impurities are implanted into the
surface region of the semiconductor-substrate 10 with the spacer
layer 17, the word gate electrode 20, and the word gate insulating
film 15 as a mask to form a low-concentration diffusion layer 51a.
Then, as shown in FIG. 50, a silicon oxide film is formed on the
entire surface through the CVD method, and etched back to form a
side wall insulating film 16 on the side surfaces of the spacer
layer 17, the control gate electrode 30, and the ONO film 11 and on
the side surface of the word gate insulating film 15. Thereafter,
as shown in FIG. 51, impurities are implanted into the surface
region of the semiconductor substrate 10 with the side wall
insulating film 16, the spacer layer 17, the word gate electrode
20, and the word gate insulating film 15 as a mask, to form a
high-concentration diffusion layer 51b. The low-concentration
diffusion layer 51a and the high-concentration diffusion layer 51b
constitute the source/drain diffusion layer 51.
[0134] Then, as shown in FIG. 52, a metal film exemplified by
cobalt is formed on the entire surface through the sputtering
method to form the silicide layers 62 and 61 on the word gate
electrode 20 and the source/drain diffusion layer 51 through a
given heat treatment, respectively. Then, as shown in FIG. 53,
after the formation of the interlayer insulating layer 19 on the
entire surface, the contact 71 that penetrates the interlayer
insulating layer 19 is formed on the source/drain diffusion layer
to form a wiring 72 on the contact 71.
[0135] With the above operation, the nonvolatile semiconductor
storage device (FIG. 45) according to the third exemplary
embodiment is manufactured.
[0136] Likewise, in the third exemplary embodiment, the same
advantages as those in the first exemplary embodiment can be
obtained. Also, in the third exemplary embodiment, since there is
applied the configuration of one bit/one cell system suitable for
the high speed operation in which the control gate electrode 30 is
disposed at only one side of the word gate electrode 20, the high
speed operation and the miniaturization of the cell size can be
performed. Further, when the configuration of the third exemplary
embodiment in which the control gate electrode 30 is disposed at
only one side of the word gate electrode 20 is applied to the
configuration of the second exemplary embodiment, still higher
speed operation can be executed (FIG. 54).
[0137] Although the invention has been described above in
connection with several exemplary embodiments thereof, it will be
appreciated by those skilled in the art that those embodiments are
provided solely for illustrating the invention, and should not be
relied upon to construe the appended claims in a limiting
sense.
[0138] Further, it is noted that, notwithstanding any claim
amendments made hereafter, applicant's intent is to encompass
equivalents all claim elements, even if amended later during
prosecution.
[0139] It is apparent to one skilled in the art that the present
invention may be changed or modified without departing from the
spirit and scope of the apparatus claims that are indicated in the
subsequent pages as well as methods that are indicated below.
[0140] AA. A method for manufacturing a nonvolatile semiconductor
storage device, comprising:
[0141] sequentially forming a charge storage layer, a conductive
layer, and a mask layer above a semiconductor substrate;
[0142] sequentially removing the mask layer, the conductive layer,
and the charge storage layer to form a trench;
[0143] covering an inside of the trench with an insulating
layer;
[0144] forming a word gate so as to fill in the trench whose inside
is covered with the insulating layer;
[0145] removing the mask layer;
[0146] forming a spacer layer so as to cover the conductive layer
and the word gate;
[0147] etching the spacer layer to form a sidewall spacer above a
side of the word gate via the insulating layer; and
[0148] removing the conductive layer and the charge storage layer
with the sidewall spacer as a mask to form a control gate.
[0149] BB. The method according to method AA, wherein the forming
of the charge storage layer, the conductive layer and the mask
layer comprises forming a silicide layer on the conductive
layer.
[0150] CC. The method according to method AA, wherein the charge
storage layer includes a laminated layer of a first silicon oxide
layer, a silicon nitride layer and a second silicon oxide
layer.
[0151] DD. The method according to method AA, further comprising
removing one of the spacer layers formed on both sides of the word
gate before the removing the conductive layer and the charge
storage layer.
[0152] EE. The method according to method AA, further comprising
implanting an ion to form a diffusion layer and a second diffusion
layer on the semiconductor substrate,
[0153] wherein the charge storage layer and the word gate are
disposed between the first diffusion layer and the second diffusion
layer.
[0154] FF. The method according to method AA, wherein a top surface
of the spacer layer is lower as the top surface of the spacer layer
is farther from the word gate.
[0155] GG. The method according to method AA, wherein a width of
the spacer layer is narrower as the width of the spacer layer is
farther from the control gate.
[0156] HH. The method according to method AA, wherein a height of
the spacer layer from a top surface of the control gate is lower as
the top surface of the spacer layer is farther from the word
gate.
* * * * *